trick/trick_source/sim_services/Integrator/unittest/ISat.cpp

#include "Integrator.hh"
#include <math.h>
#include <iostream>

// This is from matrix_macros.h in Trick.
      /* matrix times vector : prod[i] = mat[i][j] * vect[i] */
#define MxV( prod , mat , vect ) { \
   prod[0] = mat[0][0] * vect[0] + mat[0][1] * vect[1] + mat[0][2] * vect[2] ; \
   prod[1] = mat[1][0] * vect[0] + mat[1][1] * vect[1] + mat[1][2] * vect[2] ; \
   prod[2] = mat[2][0] * vect[0] + mat[2][1] * vect[1] + mat[2][2] * vect[2] ; \
}

// GRAVITATIONAL_CONSTANT (Nm2/kg2)
#define GRAVITATIONAL_CONSTANT 6.67e-11
// LUNAR_MASS (kg)
#define LUNAR_MASS   7.36e22
// LUNAR RADIUS (m)
#define LUNAR_RADIUS 1737400.0

#define RADIANS_PER_DEGREE 0.0174532925

typedef struct {
    double mass;
    double pos[3];
    double vel[3];
    double acc[3];
} SATELLITE;

typedef struct {
    double radius;
    double mass;
} PLANET;

typedef struct {
    double semi_major_axis;     /* (m)  */
    double eccentricity;        /* (--) */
    double inclination;         /* (r)  */
    double argument_of_perigee; /* (r)  */
    double right_ascension;     /* (r)  */
    double true_anomaly;        /* (r)  */
} ORBITAL_ELEMENTS;

void calc_gravity( SATELLITE * S,
                   PLANET    * P,
                   double    * G ) {

   double distance;
   double pos_hat[3];
   double g_force_mag;

   // Calculate Gravitational Force
   distance = sqrt( S->pos[0] * S->pos[0] +
                    S->pos[1] * S->pos[1] +
                    S->pos[2] * S->pos[2] );

   pos_hat[0] = S->pos[0] / distance ;
   pos_hat[1] = S->pos[1] / distance ;
   pos_hat[2] = S->pos[2] / distance ;

   g_force_mag = ( GRAVITATIONAL_CONSTANT * P->mass * S->mass ) / ( distance * distance ) ;

   G[0] = g_force_mag * - pos_hat[0] ;
   G[1] = g_force_mag * - pos_hat[1] ;
   G[2] = g_force_mag * - pos_hat[2] ;

}

// 
// Reference: ISS SIGI Attitude Processor Orbit Equations EG2/Rodolfo Gonzalez 20 Aug 2003
void orb_elem_to_intl( ORBITAL_ELEMENTS * O,          /* IN  */
                       PLANET           * P,          /* IN  */
                       double           * R_intl,     /* OUT */
                       double           * V_intl ) {  /* OUT */

    double ra, wp, in ;
    double M_pci_perif[3][3];   /* Perifocal --> Inertial transform */
    double semi_latus_rectum;
    double r_magnitude;
    double r_perifocal[3];
    double v_perifocal[3];
    double v_mag;

    semi_latus_rectum = O->semi_major_axis * ( 1.0 - O->eccentricity * O->eccentricity );

    r_magnitude = semi_latus_rectum / (1.0 + O->eccentricity * cos( O->true_anomaly ));

    r_perifocal[0] = r_magnitude * cos( O->true_anomaly);
    r_perifocal[1] = r_magnitude * sin( O->true_anomaly);
    r_perifocal[2] = 0;

    v_mag = sqrt( GRAVITATIONAL_CONSTANT * P->mass / semi_latus_rectum);

    v_perifocal[0] = v_mag * (-sin(O->true_anomaly));
    v_perifocal[1] = v_mag * (O->eccentricity + cos(O->true_anomaly));
    v_perifocal[2] = 0;

    ra = O->right_ascension;
    wp = O->argument_of_perigee;
    in = O->inclination;

    M_pci_perif[0][0] =  cos(ra)*cos(wp) - sin(ra)*cos(in)*sin(wp) ;
    M_pci_perif[0][1] = -cos(ra)*sin(wp) - sin(ra)*cos(in)*cos(wp) ;
    M_pci_perif[0][2] =  sin(ra)*sin(in);

    M_pci_perif[1][0] =  sin(ra)*cos(wp) + cos(ra)*cos(in)*sin(wp) ;
    M_pci_perif[1][1] = -sin(ra)*sin(wp) + cos(ra)*cos(in)*cos(wp) ;
    M_pci_perif[1][2] = -cos(ra)*sin(in) ;

    M_pci_perif[2][0] = sin(in)*sin(wp) ;
    M_pci_perif[2][1] = sin(in)*cos(wp) ;
    M_pci_perif[2][2] = cos(in) ;

    MxV( R_intl , M_pci_perif , r_perifocal) ;
    MxV( V_intl , M_pci_perif , v_perifocal) ;

}





void deriv(SATELLITE *S, PLANET *P) {

    double    gforce[3];

    calc_gravity(S, P, gforce );

    S->acc[0] = gforce[0] / S->mass ;
    S->acc[1] = gforce[1] / S->mass ;
    S->acc[2] = gforce[2] / S->mass ;

}

int main(int argc, const char* argv[]) {

    SATELLITE satellite;
    PLANET    planet;
    ORBITAL_ELEMENTS orbital_elements;

    long      tick = 0;
    double    seconds_per_tick = 1.0;
    double    sim_time = 0.0;

    // Initialization
    satellite.mass = 100;
    planet.mass   = LUNAR_MASS;
    planet.radius = LUNAR_RADIUS;

    orbital_elements.semi_major_axis = 2000000; // meters 
    orbital_elements.eccentricity = 0.2;
    orbital_elements.inclination = 5.0 * RADIANS_PER_DEGREE;
    orbital_elements.argument_of_perigee = 0.0;
    orbital_elements.right_ascension = 0.0;   // radians
    orbital_elements.true_anomaly = 0.0;      // radians

    orb_elem_to_intl( &orbital_elements,
                      &planet,
                      satellite.pos,
                      satellite.vel);

    Trick::Integrator *I = getIntegrator( Euler, 6, 1.0);

    do { // sim loop
        sim_time = tick * seconds_per_tick ;
        std::cout << "sim_time = " << sim_time << std::endl;

        do { // Integration Loop

            I->time = sim_time;

            std::cout << "step #" << I->intermediate_step << std::endl; std::cout.flush();

            std::cout << "deriv ...";  std::cout.flush();
            deriv( &satellite, &planet);
            std::cout << "done." << std::endl; std::cout.flush();

            std::cout << "loading state ..."; std::cout.flush();
            I->state[0] = satellite.pos[0];
            I->state[1] = satellite.pos[1];
            I->state[2] = satellite.pos[2];
            I->state[3] = satellite.vel[0];
            I->state[4] = satellite.vel[1];
            I->state[5] = satellite.vel[2];
            std::cout << "done." << std::endl; std::cout.flush();

            std::cout << "loading state deriv ..."; std::cout.flush();
            I->deriv[I->intermediate_step][0] = satellite.vel[0];
            I->deriv[I->intermediate_step][1] = satellite.vel[1];
            I->deriv[I->intermediate_step][2] = satellite.vel[2];
            I->deriv[I->intermediate_step][3] = satellite.acc[0];
            I->deriv[I->intermediate_step][4] = satellite.acc[1];
            I->deriv[I->intermediate_step][5] = satellite.acc[2];
            std::cout << "done." << std::endl; std::cout.flush();

            std::cout << "integrate" << std::endl; std::cout.flush();
            I->integrate();
            std::cout << "done." << std::endl; std::cout.flush();

            satellite.pos[0] = I->state_ws[I->intermediate_step][0];
            satellite.pos[1] = I->state_ws[I->intermediate_step][1];
            satellite.pos[2] = I->state_ws[I->intermediate_step][2];
            satellite.vel[0] = I->state_ws[I->intermediate_step][3];
            satellite.vel[1] = I->state_ws[I->intermediate_step][4];
            satellite.vel[2] = I->state_ws[I->intermediate_step][5];

        } while ( I->intermediate_step);

        std::cout << "(" << satellite.pos[0] <<","<< satellite.pos[1] <<","<< satellite.pos[2] << ")" << std::endl;

        tick++;
        
    } while (sim_time < 10.0);
}